A wide range of articles or objects are increasingly being fabricated or formed by filament winding processes, the articles ranging from large missile or spacecraft casings to medium size pressure vessels and even small couplings or fittings. The filaments used in such processes also are widely varied, including fiberglass, graphite, Kevlar and the like. Similarly, a variety of matrix binders are used to hold the filaments in a set or cured composite which is wound in the shape of the article or object, ranging from thermosetting epoxy resins which are heat-cured, to thermoplastic coatings about or impregnated in the filaments.
The art of winding filaments with thermoplastic matrix binders has become increasingly in demand. Such thermoplastic binders are easy to manage and eliminate the step of an independent curing process conventionally used with epoxy resin binders after the article has been wound. Thermoplastic coatings or impregnated binders can be heated and rendered soft or melted during the actual winding process itself and subsequent curing steps are not necessary. For instance, copending application Ser. No. 870,655, filed May 30, 1986, to Ho, and assigned to the assignee of this invention, shows a method of filament winding using thermoplastic impregnated filaments wherein an oven is used to generally heat the area about a mandrel upon which the filaments are wound. General heating may also include heating the mandrel itself. Often, a preheating step is used to at least partially melt or soften the thermoplastic matrix immediately before the filaments are wound on the mandrel. Details of the above process are incorporated herein by reference to the aforesaid application.
Another method of winding with thermoplastic impregnated filaments is shown in copending application Ser. No. 847,911, filed Apr. 13, 1986, to Sudduth et al, and assigned to the assignee of this invention. Rather than requiring a complete general heating of the area about the mandrel on which the filaments are wound, that process utilizes localized heating means to limit the heating to the immediate area about the filament as it is wound onto the mandrel. General heating requires a great deal of energy, and the localized heating process as disclosed in that application obviates such requirements. Ultrasonic means and preheating means also may be utilized as disclosed therein.
In all of the processes, including those described above, considerable energy and expensive apparatus are required to carry out the processes even though the processes have distinct advantages over filament winding with epoxy resins which must be subsequently cured. The present invention is directed to providing a novel method and apparatus for applying thermoplastic impregnated filaments or the like in a greatly simplified, significantly cheaper and safer process.